pete williams is reporting that federal officials say they believe they know who sent the letters to st senate and the white house but no arrest has been made yet. they're waiting for test results. >> we're going to hear from jay carney sometimes in the past few minutes about either boston or developments in washington or both. just as someone who reports to the area every day, can you give us an idea of how different security looked? >> it doesn't have the mi militarized feel. yesterday we had a parade that didn't appear that different at all. today coming up here to capitol hill all of the trash cans in the parks have been taking off their bases and knocked over on their sides. clearly they're going to go around and collect those and provide one less place for somebody to hide a gis and staffers are feeling jittery. we have a couple of these incidents. you can imagine people are on heightened alert. a lot of peoplery saying it feels reminiscent of the post 9/11 era. >> don't go too far. they think they may know who sent at least some of these letters. can you add anything to it? >>